GREENVILLE, S.C. — In their first formal debate, a group of GOP presidential contenders on Thursday hailed the death of Sept. 11 mastermind Osama bin Laden but said that long-awaited success has not tempered their view that President Obama has been weak in his international leadership.

Obama deserves credit for “making a tough call and being decisive as it related to finding and killing Osama bin Laden,” said former Minnesota governor Tim Pawlenty. But he added: “That moment is not the sum total of America’s foreign policy.”

Pawlenty contended that Obama as a candidate had opposed techniques that “led to bin Laden’s being identified and killed” — an apparent reference to harsh interrogation tactics — and he faulted the president for ceding the United Nations too much decision-making authority in Libya.

“If you look at what President Obama has done right in foreign policy,” added former Pennsylvania senator Rick Santorum, “it has been a continuation of Bush policies.”

The fact that foreign policy questions dominated the kickoff debate, however, was evidence of how bin Laden’s killing has thrown the GOP presidential field off balance, if only temporarily. Domestic economic concerns had been expected to drive the presidential race.

To the degree they discussed the primary issue in the campaign — jobs and the economy — the candidates demonstrated few differences and focused instead on attacking Obama for failing to turn things around.

Only five potential candidates showed up for the debate, which was co-sponsored by Fox News Channel and the South Carolina Republican Party. Among them, Pawlenty is the only one considered to have a strong shot at the nomination. In addition to San­torum, the others were Rep. Ron Paul (Tex.), former New Mexico governor Gary Johnson and former Godfather’s Pizza chief executive Herman Cain, who is also a radio talk show host.

Among the missing, though considered likely to run, were former Massachusetts governor Mitt Romney and former House speaker Newt Gingrich.

There are a host of other possibly strong contenders in varying stages of deciding whether to make a bid: former Arkansas governor Mike Huckabee, Indiana Gov. Mitch Daniels, and former Utah governor and ambassador to China Jon Huntsman.

The day also brought a reminder of what the ultimate winner of the GOP nomination will be up against in trying to unseat an incumbent president, and why history has shown it is so difficult to beat one.

The power of the office was on abundant display as President Obama laid a wreath at Ground Zero in New York, honoring the dead of the Sept. 11 attacks four days after U.S. Navy SEALs raided bin Laden’s compound in Pakistan and killed the al-Qaeda leader.

Pawlenty has lately been taunting his would-be opponents to “get off the sidelines.”

In a commentary Thursday on the Daily Caller, a conservative Web site, Pawlenty warned: “Some candidates are skipping tonight’s Republican debate in South Carolina because they believe it’s ‘too soon’ to begin the presidential campaign against Barack Obama. I only hope that it’s not too late.”

Though the president has been saddled with a weak economy and an unpopular health-care plan, Pawlenty wrote, “He is an excellent campaigner who is already working hard to build the most expensive campaign in American history. Republicans will only win if we unite behind our conservative values and start the campaign against him now.”

The candidates were asked about their absent would-be opponents, and all of them did their best to stick to former President Ronald Reagan’s rule of not speaking ill of fellow Republicans.

Asked, for instance, whether his prospects would suffer if Huckabee decided to enter the race, Pawlenty said, “I love the Huck. I know him. He’s a good colleague of mine, [but] as I get better known, I’m getting more and more support and I think the momentum is on my side.”

Santorum, meanwhile, took a dig at Daniels’s suggestions that the Republican Party should keep its focus on economic issues and put less emphasis on social ones.

“Anybody who would suggest we call a truce on moral issues doesn’t understand what America’s all about,” Santorum said.

The presence of two libertarians — Paul and Johnson — in the relatively small group gave the debate a different emphasis, indeed one that is at odds with the GOP mainstream.

Paul expressed support for legalizing heroin, for instance, and Johnson restated his call for legalizing marijuana. And both are against continuing the war in Afghanistan.